How to cplot() a conditional function

Question

I want to plot this function defined on complex numbers: if floor(Re(z))%2==0, f(z)=z else f(z)=sin(z)

I tried to code this:

import cplot
import math
import numpy as np

def f(z):
    if math.floor(np.real(z)[0])%2==0:
        res =z
    else:
        res=np.sin(z)  
    return res

plt = cplot.plot(f, (-10, +10, 3000), (-10, 10, 3000),5)
plt.show()

But it didn't work, the program completely ignores the existence of the sin function and I don't know why.

I thought this was because of my usage of math. and np. so I tested a simpler function:

if Re(z)>=0, f(z) =z, else f(z)= sin(z)

import cplot
import numpy as np

def f(z):
    if np.real(z)[0]>=0:
        res =z
    else:
        res=np.sin(z)  
    return res

plt = cplot.plot(f, (-10, +10, 3000), (-10, 10, 3000),5)
plt.show()

This time the existence of z was completely ignored.

I thought maybe the problem came from the [0] in np.real(z)[0] but removing it would yield an error

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I used them and the result is still the same, it completely ignores z in my second code, also the problem seems to be in the > sign; if I change it to < it completely ignores the sin.

"completely ignore the existence of the sin function": what do you mean with "ignore"? Do you mean a statement is not executed? What is the result of your debugging session? — trincot
– trincot, Commented Aug 1, 2024 at 7:53
@trincot It plot the other function (z) and didn't plot the sin at all as if I never wrote it. — pie
– pie, Commented Aug 1, 2024 at 7:54
What happens when you run this in a debugger and set breakpoints and inspect variables? Surely you can monitor what exactly executes in f? — trincot
– trincot, Commented Aug 1, 2024 at 7:59

tripleee · Accepted Answer · 2024-08-01 11:56:36Z

1

The function you plot should return an array of results, not just the static result for the first item in the input array.

I'm not a Numpy person, but based on Applying a function along a numpy array I would try something like

def f(x):
    if np.real(x) >= 0:
        res = x
    else:
        res = np.sin(x)  
    return res

f_v = np.vectorize(f)
plt = cplot.plot(f_v, (-10, +10, 3000), (-10, 10, 3000),5)
plt.show()

I'm sure this could be rewritten more elegantly but at least this should show the direction.

edited Aug 1, 2024 at 11:56

answered Aug 1, 2024 at 8:12

tripleee

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Comments

Naveed Ahmed · Accepted Answer · 2024-08-01 08:07:45Z

1

There is a a problem in how you are treating z. You are treating it as a regular array and not as a complex number. So, here is how it should possibly be

def f(z):
   if np.floor(z.real) % 2 == 0:
       res = z
   else:
        res = np.sin(z)
   return res

answered Aug 1, 2024 at 8:07

Naveed Ahmed

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